Conventional displays are currently produced in several technology types, including cathode-ray tube (CRT), light emitting diode (LED), liquid crystal displays (LCDs), and projection display systems. CRT displays utilize a vacuum tube and an electron beam source mounted behind a luminescent screen to generate an image. LED displays include an array of light emitting pixels that are individually addressed by an active or passive backplane (addressing circuitry) to generate an image. Projection display systems utilize a projection device that projects an image onto a passive, typically white screen, which is reflected back toward an audience.
Large area display applications (e.g., greater than 60″) are most commonly implemented using projection display technology due to their lower cost and power consumption. CRT and LED displays are typically cost effective to product and operate when relatively small in size, but are typically too heavy and/or require too much power to operate when produced in a large area display format. In contrast, projection display systems are more easily scalable to larger area formats simply by increasing the size of the relatively low-cost, light weight screen, and increasing the size of the image projected on the screen.
Projection displays include arc lamp displays and laser-based projection displays. Early projection display systems used a white light source, such as a xenon arc or halogen lamp, that illuminates one or more light valves or spatial light modulators with appropriate color filtering to form the projected image, thus facilitating the production of relatively inexpensive, scalable, low-power, large area displays. However, such arc lamp projection displays are often criticized because of poor picture sharpness, a small viewing angle, and because the projected picture is readily “washed out” by bright ambient light. More recently, laser-based projection displays have been introduced that operate in a manner similar to arc lamp projection displays, but avoid the picture quality issues by utilizing relatively bright red, green and blue laser beams to generate much higher quality projected images. A fundamental problem with large-area laser-based displays, however, is the laser power that is required to generate a suitable picture. The power required (e.g. >1 W) is well beyond that which is considered safe in consumer applications. In addition, inexpensive lasers with sufficient power are not yet available, especially at the green and blue wavelengths, thus making laser-based displays significantly more expensive than arc lamp displays. Moreover, even high-powered displays become washed out in high ambient light due to their use of white screens (which are used to limit the required laser brightness). Dark or black screens may be used to prevent this washout problem, but this only increases the power requirements on the lasers, making the overall display system impractically expensive.
What is needed is a scalable, large area display apparatus that provides a picture equal to or greater than state of the art laser-based projection displays, but is less expensive to produce and operate, and avoids the safety concerns associated with the use of high powered lasers.